Xenon Discharge Research Articles

Far-Ultraviolet Photolysis of Nitric Oxide

Nitric oxide has been photolyzed in the region 1550–1650 Å using a hydrogen discharge and at 1470 and 1236 Å using xenon and krypton discharges, respectively. The products at all wavelengths are N2 and NO2. At 1470 Å small amounts of N2O are produced. The quantum yield of N2 increases over the nitric oxide pressure range 5–900 mm from ∼0.2–0.5 and also with added inert gas. Quantum yields of NO2 production and of NO decomposition increase in a similar manner, and the wavelength has no profound effect. Since 1236-Å light ionizes NO, it is concluded that the recombination of NO+ and an electron leads to an excited molecule which decomposes, as it does at 1600 and at 1470 Å, into N and O atoms. These react with excess NO producing N2 and NO2.

AMPLIFICATION OF RADIO-WAVES IN PARTIALLY IONIZED GASES

The amplification of radio-frequency wave is observed in partially ionized gases, having large Ramsauer effect, in the absence of magnetic field. This paper gives results showing power gains of more than 4 db at 60 Mc/s and 3 db at 20 Mc/s in a xenon discharge plasma. By adjusting a dc grid current of a triode-type discharge tube, a strong attenuation or an amplification of an applied r f wave or an intense r f emission with no input signal is observed. This phenomenon occurs in pulses at some definite phase of a l f oscillation existing in the d c discharge when the detecting frequency is smaller than the critical one, which is somewhat smaller than the collision frequency of the plasma electrons. It is considered that experimental results are interpreted as a phenomenon of the negative absorption due to the stimulated brems-strahlung in partially ionized gases.

Far-Ultraviolet Photolysis of Acetone

A survey of the trends in acetone decomposition in the range from the near-ultraviolet photolysis to gamma radiolysis has been made using a xenon discharge (1470 and 1295 Å) and a krypton discharge (1236 and 1165 Å) for room temperature photolysis. The variation of the ratios to CO of products as a function of acetone pressure and wavelength has been noted. Analysis of the mixed products from mixtures of acetone and acetone-d6 presents evidence for methyl radicals in the production of ethane, of hot methyl radicals in the production of methane and of hydrogen atoms in the production of hydrogen. Deviation from the H2—D2 equilibrium indicates molecular hydrogen elimination. The conclusions are confirmed by scavenger studies using propylene, iodine, and oxygen, as well as by the effects of added xenon and neon. The results are consistent with the existence of two excited states of acetone, the higher state eliminating either H or H2; the lower state, methyl. The far-ultraviolet photolysis appears to be closer in over-all behavior to the gamma radiolysis than to the near-ultraviolet photolysis and the trend of the decomposition may be explained by the increase in energy of the radiation.

Laser action in singly ionized krypton and xenon

Laser oscillation has been observed in pulsed krypton and xenon discharges on 21 wavelengths spanning the visible portion of the spectrum. All lines observed arise from transitions between levels of the singly-ionized state of the atoms (KrII, XeII spectra). The wavelengths and tentative level assignments are given in Table I for krypton and Table II for xenon. Oscillation between energy levels of ions has previously been reported for mercury [1] and argon [2]. The levels reported here are analogous to those observed in argon. The xenon transitions are all s → p or s’ → p’, while the krypton transitions are predominantly of this type, but include one p → d two p’ → d.

Stresses in Molybdenum Foil-to-Silica Glass Seal

Silica glass, owing to its high thermal endurance, is used for bulbs of high pressure mercury discharge lamps, xenon discharge lamps or incandescent iodine lamps. Thermal expansion of silica glass is so low that metals or alloys with comparably low expansion coefficients to seal with are not found. Sealing with thin molybdenum foils is an usual technique in lamp manufacturing industry. Stresses in such a seal caused by expansion difference between metal and glass are reduced by plastic flow of the foil.Stresses in experimental seals were studied photoelastically. Foils used were 20μ thick. Severe and mild stress concentrations in glass were observed near the edge and the surface of foil respectively. Change of distribution of stresses with temperature was rather complicated, showing some hysteresis phenomena caused by plastic and elastic deformation of foil and viscous flow of glass. Stresses in glass were evaluated to be less than 1kg/mm2 except near the edge of foil. Effect of plasticity of foil on distribution or reduction of stresses were discussed.

Stimulated Infrared Emission from Trivalent Uranium

Stimulated infrared emission from uranium(III) in CaF/sub 2/ was studied using a single CaF/sub 2/ crystal with 0.05 mole% uranium and silver films on both ends. The crystal was cooled with liquid helium and excited by a pulsed xenon discharge, and the radiation was isolated at 2.5 mu and detected. Oscilloscope traces of the detector response showed the ratio between the stimulated emission and the background light to be>1000 and relaxation oscillations to be present, the number of spikes increasing with the power of the xenon discharge. (D.L.C.)

A Machine for High Speed Printing from 35mm Colour Transparencies

AbstractA machine for making colour prints at high speed from 35mm. transparencies employs one operator to load the transparencies into a storage magazine, from which they are fed into the machine automatically and after printing are unloaded by a second operator. Information relating to each transparency loaded into the magazine is punched on to standard 5-hole paper tape. Colour quality of the light is controlled by varying the phase relationship between synchronously rotating sectored filter discs, and the light output of an Xenon discharge lamp, both being operated from the same A.C. supply.

The formation of molecular hydrogen through photolysis of water vapor in the presence of oxygen

1. A light source was constructed for the investigation of the photolysis of water vapor. A xenon discharge arc of a pressure of about 50 mm in a thin wall quartz tubing was used. 2. Molecular hydrogen formed from water vapor in the presence of other gases was measured by employing tritium as a tracer. A vacuum system was constructed, allowing the separation of water vapor from hydrogen to better than 10−8 parts, and the counting of tritiated hydrogen in a Geiger counter. All measurements were carried out in a semi-quantitative way and it was found that the light source and the technique of measuring small amounts of free hydrogen by employing a tritium tracer can be used effectively for further studies of the reactions involving hydrogen and water. 3. Self-decomposition of tritiated water vapor with and without addition of oxygen was measured and was found to be negligible under the particular conditions of the experiments over periods of several months. 4. The photochemically induced exchange of tritium between tritiated water vapor and molecular hydrogen was studied. The quantum yield of this exchange was found to be under the conditions of the experiments of the order of one and probably slightly larger than one. 5. It was possible to demonstrate the formation of free hydrogen from the photolysis of water vapor in the presence of oxygen and to measure these amounts as a function of oxygen pressure. The steady state concentrations of H2 formed from water vapor by irradiation in the presence of oxygen under the influence of UV light were found to be smaller than expected. 6. Photochemical oxidation of H2 by O2 under the particular conditions of the experiments and at pressures of about one millimeter was found to have a quantum yield of the order of magnitude of one.

Recombination in Xenon and Krypton Afterglows†

ABSTRACT Electron density decay was studied in the afterglow of pulsod electrodeless microwave discharges in krypton and xenon using 3 cm equipment. Each gas contained an unknown impurity of not more than 0-5% of the other. Gas pressure was variod from 3 to 30 mm Hg and ionizing pulse power from 1-5 to 22-5 kw. The xenon afterglow was unaffected by the krypton impurity at pressures above 5 mm Hg and lod to a recombination coefficient of 23 x 10−1 cm3 ion sec at 10 mm Hg. This coefficient increased with pressure above 10 mm Hg, probably caused by pressure limitations on tho microwave method. It is suggested that the krypton afterglow was greatly affected by charge transfer to the xenon impurity. A recombination coefficient of not greater than ion 1. 1×10−6 sec is deduced for krypton.

New Method of Flow Visualization for Low-Density Wind Tunnels

A new method of visualizing low-density flows is described which employs the absorption by oxygen of radiation in the wavelength region 1400 A to 1500 A. It was developed for use in the low-density supersonic continuous flow wind tunnels at Berkeley because the conventional methods (shadowgraph, schlieren, and interferometer) were predicted to have inadequate sensitivity at the unusually low densities in the test section. A xenon discharge is used for the source of radiation, its 1470 A resonance line being isolated by a calcium fluoride vacuum monochromator. A 26 mm diameter beam of parallel radiation is passed through the test section where it is absorbed more or less depending on the oxygen density along the radiation path. The center of the test section is then focused by a calcium fluoride vacuum camera on an ultraviolet-sensitive photographic plate. Pictures of shock waves from cylinders ⅛ and ¼ inch in diameter and from a 60° ⅜ inch wedge were obtained with exposure times of about 4 minutes. Development of a stronger source would reduce the exposure time appreciably. This oxygen absorption method is shown to be suitable, in principal, for general wind tunnel work where the absolute pressures are below about 1 mm Hg.

A Stroboscopic Mercury Vapour Light Source

Beeson and Webb1 have recently described a xenon discharge lamp for optical systems which is capable of either continuous or flash operation.

A Discharge Illuminant for Optical Systems capable of either Continuous or Flash Operation

IT is sometimes desired to illuminate an object in an optical system at one level for general examination and at a momentarily higher level for photographic recording. The development of a combined flash and continuous source lamp offers a novel method for doing this. The high-pressure mercury-vapour compact-source lamp, the characteristic high brightness of which is well known, has successfully been used under pulse conditions to provide high levels of illumination for high-speed cine photography1,2; this type of lamp has also been used as a condenser flash-discharge source to give high-intensity short-duration flashes of light. Recently a small xenon discharge lamp has been developed which provides a useful amount of light for such purposes as photo-micrography, and can, in addition, be switched at will from the steady arc to a condenser flash-discharge with a flash duration of less than 50 microsec. The xenon discharge gives excellent colour rendering under both conditions of operation.

A new power stroboscope for high-speed flash photography

A power stroboscope has been developed for high-speed flash photography at picture repetition rates from 100–4000 pictures/sec, the duration of each flash being 5 microsec. The control circuit uses a hydrogen thyratron to trigger the tube discharge, and the energy is supplied to the lamp at 12 kV. The storage capacitor of 0.1 μF delivers 4 joules to the lamp.During the development it was found that the light emission from a low-pressure xenon-filled tube persisted for a considerable time after current had ceased to flow. This afterglow in xenon discharges is greatly reduced by an increase in gas pressure and other changes in the physical design of the lamp.The stroboscope can be used for direct photography with a drum camera, or it can be synchronized with the optical compensation element of an image-compensated camera.Some examples of the application of the system to cavitation research are given.